The present invention relates to devices for imprinting various patterns in concrete that is still wet and soft after a slab has been freshly poured and smoothed.
In the past, imprinting has been accomplished in different ways. The most popular way is to imprint by hand with various types of flat forms that are pressed into the concrete before it has set. These forms vary in size, but are generally small enough for one man to handle.
There are a number of drawbacks to any hand-forming method. One drawback is that it is very time consuming in that the form has to be pressed into un-set concrete by the worker, then the form has to be picked up and realigned with the imprint just made. This process is repeated until the entire slab has been imprinted.
A second drawback of such a hand-forming method is caused by the time consumptive method described above. A large slab of concrete would have to be made in several pours since the length of time it would take to imprint by hand would allow the slab to set too hard before the slab could be finished with the imprinting process.
There are some known repeating pattern imprinting devices. A first such device is disclosed in U.S. Pat. No. 3,832,079. The device disclosed in that patent has some major drawbacks which make it impractical, if not impossible, to use. First of all, the device includes a motorized tractor vehicle which must be driven on and over the top of a poured slab. In order to accomplish this, because of its heavy weight, the operator must wait for the slab to set up hard enough to support the device. Once the concrete has set to this point, any grid forced into it would cause bulged, torn, or broken edges on the concrete surface where each grid penetrates. This will happen even if a plastic buffer or releasing agent is used as suggested in that disclosure. Because of the weight of the vehicle, this device cannot be used on soft concrete without the vehicle sinking below the surface.
A second type of repeat pattern imprinter is disclosed in U.S. Pat. No. 4,105,354. This device has a number of significant drawbacks as well. First, it is stated in the disclosure that the imprint should be approximately three quarters of an inch deep. An imprint this deep would weaken the slab. To make up for the weakening of the slab, the entire slab would have to almost one inch thicker. The device disclosed in this patent is a large wheel or cylinder which is large enough to accommodated a worker in a walking position therein. The workers are to walk and grasp interior portions of the cylinder to cause it to roll along a freshly poured slab. Although the disclosure suggests that workmen can direct this wheel from the inside, the fact is that once inside the wheel, the worker can only make the device go forward or backward. There is no way for the worker to steer right or left. The worker can therefore only go where the wheel takes him. If the worker is to steer, he must step outside of the wheel and apply force on the side of the wheel.
Further, the disclosed device has to be very large in order to a man to fit inside. Therefore, even if it were built out of aluminum, which would be quite costly, its size and weight would make it very awkward to handle. Further, because the grid is open and due to the extreme weight of the wheel and workmen inside of it, there is no way to control the device's depth on a slab of freshly poured and still soft concrete. A device of this size would sink beyond the surface of the concrete, even without any workers in it.
It would therefore be necessary for the concrete to at least partially set before such a device could be used. Any device that requires the workers to wait for the concrete to become partially set is not practical. Because timing is so critical in the setting of a concrete slab, waiting for the concrete to become partially set would be a guessing game, even for a person with experience. Also, the workmen would have to remain on the job site waiting for the concrete to partially set. If the timing is off, the concrete would either be too soft, thus causing the device to sink below the surface, or if the concrete becomes too hard, the device will not provide the necessary imprint, even with a number of people within the wheel.
Since this device can be used only when the concrete has partially set, there is a danger of getting bulged, torn, or broken edges at each grid penetration on the concrete surface. The cost of having workmen wait on a job site to permit the concrete to partially set up would become quite expensive.
Finally, even if this device could be used, with a person inside, on freshly poured concrete, there would be a very messy drawback. Because of the open nature of the grid, concrete is going to be carried up and over by the open grid and dropped through onto the workmen inside. Even if the workmen were to be wearing protective clothing, there would still be a considerable mess generated by this device.
Therefore, it would be an improvement in the art if there were provided a device which could be used to imprint various impressions on freshly poured concrete in a fast and efficient manner, without waiting for the concrete to set up and to allow the users of the imprinting device to guide the device in a controlled fashion.